U.S. patent number 5,943,333 [Application Number 08/624,578] was granted by the patent office on 1999-08-24 for radio communications device and method.
This patent grant is currently assigned to Motorola. Invention is credited to Jonathan Alastair Gibbs, William Neil Robinson, Anthony P Van Den Heuvel, Nicholas William Whinnett.
United States Patent |
5,943,333 |
Whinnett , et al. |
August 24, 1999 |
Radio communications device and method
Abstract
A radio communications device is arranged to communicate time
divided signals (60 and 70) over first (40) and second (50) time
discontinuous systems having first and second frame structures
respectively. Switching device (120) switches between communicating
signals (60) over the first system (40) during time periods of the
first frame structure and communicating signals (70) over the
second system (50) during time periods of the second frame
structure. Hence over a given period of time the device
simultaneously communicates time divided signals over the first
(40) and second (50) systems.
Inventors: |
Whinnett; Nicholas William
(London, GB), Robinson; William Neil (Farnham,
GB), Gibbs; Jonathan Alastair (Southampton,
GB), Van Den Heuvel; Anthony P (Lightwater,
GB) |
Assignee: |
Motorola (Schaumburg,
IL)
|
Family
ID: |
10759541 |
Appl.
No.: |
08/624,578 |
Filed: |
July 1, 1996 |
PCT
Filed: |
July 27, 1995 |
PCT No.: |
PCT/EP95/03009 |
371
Date: |
July 01, 1996 |
102(e)
Date: |
July 01, 1996 |
PCT
Pub. No.: |
WO96/05707 |
PCT
Pub. Date: |
February 22, 1996 |
Foreign Application Priority Data
Current U.S.
Class: |
370/345;
455/553.1; 370/341; 455/12.1; 455/557 |
Current CPC
Class: |
H04W
36/14 (20130101); H04B 1/406 (20130101); H04W
36/18 (20130101) |
Current International
Class: |
H04Q
7/32 (20060101); H04Q 7/38 (20060101); H04B
1/40 (20060101); H04B 007/185 () |
Field of
Search: |
;370/313,314,328,338,341,345,430,455 ;379/59,60,61 ;342/36,37
;455/425,435,450,552,557,12.1,33.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
0 577322A1 |
|
Jun 1993 |
|
EP |
|
0577322 |
|
Jan 1994 |
|
EP |
|
WO93/16549 |
|
Aug 1993 |
|
WO |
|
Other References
"Towards a Combined GSM 900 DCS 1800 System", Ph.Duplessis,
P.Simmons, Matra Communication, Rue JP Timbaud, 78392 Bois d'Arcy
France, Fifth Nordic Seminar on Digital Mobile Radio
communications, Helsinki Finland Dec. 1-3, 1992,pp. 89-92. .
"Developing Technologies For Personal Communication Networks", by
P.S. Gaskell, Electronics & Communication Engineering Journal,
Apr. 1992, pp. 53-63..
|
Primary Examiner: Olms; Douglas W.
Assistant Examiner: Hom; Shick
Attorney, Agent or Firm: Coffing; James A. Lukasik; Susan
L.
Claims
We claim:
1. A method of handoff from a first time discontinuous system to a
second time discontinuous system by a radio communications device
comprising the steps of,
establishing a call with a remote user via the first time
discontinuous system; establishing communication with the second
time discontinuous system while continuing the call via the first
time discontinuous system during a handoff period;
invoking a contention scheme to determine which of the first and
second time discontinuous systems is in communication with the
remote user during the handoff period; and
handing off from the first to the second time discontinuous system
whilst maintaining the call to the remote user via the second time
discontinuous system, wherein the contention scheme manages the
communications activities of the device during the handoff period
such that contention between the communication of the first and the
second time discontinuous systems is substantially resolved and the
call is maintained.
2. The method of claim 1, wherein the contention scheme is based on
known characteristics of the time discontinuous systems.
3. The method of claim 1, wherein if only the first time
discontinuous system has signal coding and interleaving, the
contention scheme is arranged to suspend communicating signals over
the first system in favor of the second system when a contention
occurs.
4. The method of claim 1, wherein if the first and the second time
discontinuous systems are similar, the contention scheme is
arranged to alternately suspend communicating signals from each of
the first and the second systems.
Description
FIELD OF THE INVENTION
This invention relates to a radio communications device and
particularly but not exclusively to handoff between two dissimilar
systems to which the device is communicating.
BACKGROUND OF THE INVENTION
Various digital communication networks exist worldwide and provide
various services for registered user devices. In many areas
different networks overlap and service to more than one network is
possible.
Multi-mode devices have been proposed which are able select and
register with one from a number of networks, depending on the
availability of the networks in question.
A problem with this arrangement is that a multi-mode device having
a single transmitter/receiver would not be able co-establish and
co-register on two networks simultaneously without losing data.
Therefore an already established call on one network must be
terminated before the device can switch to the other network, i.e.
the call must be relinquished.
It would be possible to build a device with two receivers, so as to
monitor and receive from two networks simultaneously, thus
preserving an established call and switching it from one network to
another. However, a device with two receivers would be expensive
and significantly larger in size than a single receiver terminal.
Similarly it would be possible to provide two transmitters for
maintaining a call on one network and establishing a call on the
second network during a handover period before dropping the call on
the first network. This too would be expensive.
This invention seeks to provide a radio communications device and
method in which the above mentioned disadvantages are
mitigated.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention a radio
communications device is provided, arranged to communicate time
divided signals over first and second time discontinuous systems
having first and second frame structures respectively, comprising:
switching means for switching between communicating signals over
the first system during time periods of the first frame structure
and communicating signals over the second system during time
periods of the second frame structure, such that over a given
period of time the device simultaneously communicates time divided
signals over the first and second systems.
Preferably the device further comprises control means for causing
the switching means to switch between communicating signals
according to a contention scheme, wherein the contention scheme
manages the activities of the device during simultaneous
communication such that any contention between the communicating
signals over the first and second systems is resolved.
The contention scheme preferably manages the switching means such
that contention is resolved between transmission communication
signals and reception communication signals when the device is not
capable of transmitting and receiving simultaneously.
Preferably the device is arranged to receive first and second time
divided signals from the first and second systems, such that over a
given period of time the device simultaneously receives time
divided signals from the first and second systems.
The device is preferably arranged to transmit first and second time
divided signals to the first and second systems, such that over a
given period of time the device simultaneously transmits time
divided signals to the first and second systems.
Preferably the management of the communication includes
substantially reducing and eliminating any data loss.
According to a second aspect of the invention a method of handoff
from a first time discontinuous system to a second time
discontinuous system by a radio communications device is provided,
comprising the steps of, establishing a call with a remote user via
the first time discontinuous system; establishing communication
with the second time discontinuous system while continuing the call
via the first time discontinuous system according to a contention
scheme, handing off from the first to the second time discontinuous
system whilst maintaining the call to the remote user via the
second time discontinuous system, wherein the contention scheme
manages the communications activities of the device during
simultaneous communication such that contention between the
communication of the first and the second time discontinuous
systems is substantially resolved and the call is maintained.
Preferably the management of the communication includes
substantially reducing and eliminating any data loss.
Preferably the contention scheme is based on known characteristics
of the time discontinuous systems, such that sufficient data is
received by the terminal to maintain communication with the time
discontinuous systems.
If only the first time discontinuous system has signal coding and
interleaving, preferably the contention scheme is arranged to
suspend communicating signals over the first system in favour of
the second system when a contention occurs.
If the first and the second time discontinuous systems are similar,
preferably the contention scheme is arranged to alternately suspend
communicating signals from each of the first and the second
systems. Preferably the time discontinuous systems include DECT
and/or GSM systems.
In this way a terminal (radio receiver) having a single receiver
and having an established call on one network may handover to
another network substantially without losing data and possibly
thereby relinquishing the call. The invention applies to time
discontinuous CDMA communications as it applies to TDMA
communications and the expression TDMA is intended to apply to time
discontinuous CDMA.
BRIEF DESCRIPTION OF THE DRAWINGS
An exemplary embodiment of the invention will now be described with
reference to the drawings in which:
FIG. 1 shows a functional block diagram of a communications system
including a preferred embodiment of a radio receiver in accordance
with the invention.
FIG.2 shows a flow chart of operation of the radio receiver of FIG.
1.
FIG.3 shows a diagram of operation of the radio receiver of FIG.
1.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Referring to FIG. 1, there is shown a communications system 10. A
telephone 20 of the system 10 is connected to a conventional public
switched telephone network (PSTN) 30. Alternatively, the telephone
network 30 could be an Integrated Services Digital Network
(ISDN).
A first network 40 is coupled to the PSTN 30 and provides a first
TDMA air-interface 60 between the PSTN 30 and any terminal device
registered with the first network 40. The first network 40 contains
a registration block 45, to be further explained hereafter.
In a similar way, a second network 50 is also coupled to the PSTN
30 and provides a second TDMA air-interface 70 between the PSTN 30
and any terminal device registered with the second network 50. The
second network 50 similarly contains a registration block 55, to be
further explained hereafter.
The first and second TDMA air-interfaces are arranged as TDMA
channels. Each TDMA carrier is divided into time frames. Each frame
is further subdivided into time slots. A particular communication
is assigned one or more slots per frame.
A terminal 100 of the system 10 has a transceiver 110, for
providing communication with the system 10 in a manner to be
further described below. A multi-mode block 120 of the terminal 100
contains a first mode block 130 and a second mode block 140, each
selectively coupled to the transceiver 110.
A controller 150, typically a microcontroller, is coupled to
control the first and second mode blocks 130 and 140, and their
selective coupling to the transceiver. In this way the first mode
block 130, if selected by the controller, provides a first mode of
operation of the terminal such that communication takes place with
the first network 40 over the first TDMA air-interface 60.
Similarly, the second mode block 140, if selected by the
controller, provides a second mode of operation of the terminal
such that communication takes place with the second network 50 over
the second TDMA air-interface 70. In this way the controller 150
switches between the air-interfaces 60 and 70. A memory 160 is
coupled to the controller 150, for storing data to be further
described below.
In operation, and with reference also to FIG.2, the terminal 100 is
initially registered with the first network 40. This may typically
be because at the time registration was made, only the first
network 40 was visible to the terminal 100. A call made between the
telephone 20 and the terminal 100 is achieved via the PSTN 30 and
the first network 40 (block 200). In this case, the first mode
block 130, controlled by the controller 150, provides the first
mode of operation of the terminal 100 in order to achieve
communication over the first TDMA air-interface 60.
During the call, the second network 50, which is not currently
registered with the terminal 100, may become available to the
terminal. This may occur in a number of ways. The terminal 100 may
move into a particular cell of the first network 40, and the memory
160 may contain data about that particular cell, to the effect that
if in this cell the second network 50 may also be available. The
controller 150 will then use gaps between sampled transmissions on
the first TDMA air-interface 60 (i.e. when the transceiver 110 is
idle) to confirm or otherwise the presence of the second network
50.
Alternatively the controller 150 may use gaps between sampled
transmissions on the first TDMA air-interface 60 (i.e. when the
transceiver 110 is idle) to search periodically for the second
network 50 via the second mode block 140 over the second TDMA
air-interface 70.
In either case if no transmission is heard from the second network
50, then the call continues via the first network 40 over the first
air interface 60. The attempted detection (block 210) is repeated
at regular intervals during the call.
In both ways the terminal 100 is capable of becoming aware that
registration to the second network 50 is possible (block 210). Once
the terminal 100 is aware of the availability of the second network
50, it must then decide which network offers the optimal service,
based on the following information.
The memory 160 contains, in data form, information about the two
networks, such as cost, features available, handover capability and
quality. This data may be received from the two networks 40 and 50
or programmed directly to the memory during manufacture or service.
Furthermore, the memory 160 contains contention resolution data, to
be further described below. Additionally, the memory 160 may also
contain data indicating a user preference, should there be one. The
controller 150 uses the network information data together with the
user preference data to select the optimal network, namely that
which offers the optimal service (block 230).
The controller 150 then decides whether the optimal network is the
currently registered one, in this case the first network 40 (block
240). If this is the case, then the call and the terminal
registration is maintained on the first network 40.
If the optimal network is not the currently registered one, (i.e.
the optimal network is the second network 50), then the terminal
100 will seek to handoff to the second network 50. However, the
terminal 100 must register with the second network 50 before
handoff from the first network 40 can take place. In order that the
call is not lost, the terminal 100 must be able to substantially
communicate with the two networks in parallel, until a
communication link has been established between the terminal 100
and the telephone 20 via the second network 50.
The controller 150 looks up a contention resolution scheme suitable
for the first and second networks 40 and 50, from the contention
resolution data in the memory 160 (block 250). The contention
resolution data may be programmed during manufacture or received
from the networks, and contains a contention resolution scheme for
every combination of two networks in order to reduce and where
possible eliminate any data loss during simultaneous communication
between the two networks.
For example, and also referring to FIG.3, the first network 40 is a
DECT network, having a single TDMA frequency 400 divided into
transmit and receive slots and the second network 50 is a GSM
network having a TDMA transmit frequency 500 divided into transmit
slots and a TDMA receive frequency 600 divided into receive
slots.
During simultaneous communication between the two networks, a
contention between slots occurs at the times indicated by arrows
410, 420, 430 and 440. At arrow 410 transmission is required on
frequencies 400 and 500 simultaneously. In a similar way at arrow
420 reception is required on frequencies 400 and 600
simultaneously. At arrows 430 and 440, transmission and reception
are required simultaneously. At all other times simultaneous
communication can take place successfully because there is no
contention between slots, and the controller 150 switches between
the frequencies 400, 500 and 600 accordingly.
The contention resolution scheme for DECT/GSM takes account of the
fact that the GSM network has coding and interleaving, whereas the
DECT network does not. Therefore, if at any one time, such as
indicated by the arrows 410, 420, 430 and 440 the terminal 100 is
being asked to communicate with both networks, the contention
resolution scheme will call for the GSM slot (or part of the GSM
slot) to be dropped, because the data carried in the GSM slot is
coded and interleaved. Hence it may be recoverable from earlier
and/or later transmissions, whereas this is not possible for the
data carried in the DECT slot. Therefore taking the case of the
arrow 420, the contention scheme will cause the controller 150 to
set the transceiver 110 to receive on frequency 400 during this
time, and not frequency 600. The contention scheme also takes into
account the presence or otherwise of a duplexer which determines if
the terminal is capable of transmitting and receiving
simultaneously. With a duplexer, the contentions indicated by the
arrows 430 and 440 (transmit and receive simultaneously) are
overcome, so there is no need to drop either of the slots in these
cases.
A contention resolution scheme for two networks which both have
coding and interleaving will take account of the number of slots
per frame of the TDMA networks, wherein the network with the higher
number is dropped if contention occurs, hence preserving a higher
proportion of data on the dropped system. Alternatively in this
case, for a particular technology combination, the contention
resolution scheme may call for the data loss to be shared between
both networks. This may be done by means of a simple alternate
dropping strategy per contention event, or by means of a more
sophisticated approach which may take in to account for example the
maximum tolerable data loss occurring per interleaving block of
each system.
The contention resolution scheme may also take account of the
nature of the data being communicated to and from each network. For
example, signalling data may have priority over traffic data.
Another example would be where the same user information is being
transmitted from each network, in which case the terminal may for a
time choose to only receive from a single network. A situation
where the second example may occur would be where a seamless
handover takes place by setting up a multiparty call and then
dropping one of the parties. While in the multiparty call state,
the terminal need only receive from one of the networks.
The contention resolution scheme taken from the contention
resolution data in the memory 160 is hence used by the controller
150 to manage the activities of the transceiver 110 during
simultaneous communication such that effective contention
resolution is achieved and communication is maintained to each
network.
The terminal 100 then attempts to register with the second network
50 (block 260), whilst maintaining the call through the first
network 40, the controller 150 using the contention resolution
described above.
If registration with the second network 50 is not successful, then
communication thereto is terminated and the second network 50
ceases to be the optimal network (block 280). The controller 150
then selects another optimal network from the known networks
available (block 230) and repeats the above steps.
If registration with the second network 50 is successful then the
controller 150 initiates a call via the second mode block 140 and
the transceiver 110 over the second TDMA air-interface 70 to the
second network 50 (block 290).
Alternatively, for some implementations of inter-system handover
the second mode block may receive a call from network 50 over the
second TDMA air-interface 70. Simultaneous communication, with
contention resolution continues during this time (blocks 300 and
310) until the call via the second network 50 is achieved. At this
point, the call is switched over from the first network 40 to the
second network 50 and the terminal 100 drops communication and
registration with the first network 40 (block 320).
The call continues to the telephone 20 via the PTSN 30, the second
network 50, the second TDMA air-interface and the second mode block
140 of the terminal 100.
It will be appreciated by a person skilled in the art that
alternative embodiments to the one described above are possible.
For example, the contention resolution data and the data about each
network which is stored in the memory 160 could be received from
each network through the transceiver 110.
The principles described above apply equally to handoff in CDMA
systems.
Direct Sequence CDMA has an inherent disadvantage compared to TDMA
when it comes to handoff in that generally, CDMA transmissions are
continuous in time. This makes inter-system monitoring,
registration and call establishment difficult without multiple
transmitters/receivers. In the RACE CODIT research programme, a
time discontinuous mode is entered into to facilitate
inter-frequency CDMA handoff. A similar process could be envisaged
for CDMA/TDMA handoff in future CDMA systems with the mobile
controlling the parameters of the discontinuous mode. Steve: this
area is probably going to be the subject of another disclosure in
the near future.
Time discontinuity also occurs in the following instances for the
Qualcomm CDMA system. In a reduced information rate mode (e.g.
during speech inactivity), the uplink is time discontinuous, with
gaps occurring for the order of 1.25 ms (or multiple thereof),
which makes switching to perform random access and signalling on
the TDMA system possible in principle if the free period and the
TDMA time slot coincide.
It will also be appreciated by a person skilled in the art that the
networks and terminal 110 could be so arranged that when a
contention is about to occur, the terminal 100 prompts one of the
networks to handover to a non-contentious slot, thereby eliminating
the contention. This is particularly applicable in the case where
the TDMA frame times are harmonically related.
Furthermore the contention resolution scheme may be used to obtain
multiple simultaneous services from the two networks 40 and 50,
such as voice and data services.
Generalisations can be readily made to the cases where a terminal
may have more than two modes; where there may be one or more
networks available on each mode; and hence where there may be more
than two networks to choose between.
* * * * *